The present invention is directed to probe stations for making highly accurate measurements of high-speed, large scale integrated circuits at the wafer level, and of other electronic devices. More particularly, the invention relates to such a probe station having a controlled-environment enclosure for isolating the wafer-supporting chuck and probe(s) from outside influences such as electromagnetic interference (EMI), moist air during low-temperature measurements, and/or light.
For sensitive probing applications where electromagnetic interference or light must be eliminated, or where probing must be conducted at low test temperatures, an enclosure must be provided surrounding the test area. For low-temperature testing, the enclosure must provide a substantially hermetic seal for the introduction of a dry purge gas, such as nitrogen or dry air, to prevent condensation of moisture onto the wafer at the low test temperature.
Two different approaches have been used in the past for providing a controlled-environment enclosure. One approach has been to provide a large enclosure which surrounds the entire probe station, including its chuck and/or probe positioning mechanisms, as exemplified by the controlled-environment enclosures marketed by the Micromanipulator Company, Inc. of Carson City, NV and Temptronic Corporation of Newton, MA. However such large enclosures have several drawbacks. One of these is that they require the user to manipulate the station controls through the confines of rubber gloves mounted on the enclosure, making set-up and operation of the probe station more difficult and time-consuming for the operator. Another drawback is that the large volume of these enclosures requires a large volume of dry purge gas, requiring a correspondingly high charging time after each unloading and loading sequence, and a correspondingly high cost of the purge gas. These large enclosures also occupy an excessive amount of valuable laboratory space. Finally, where the enclosure surrounds the entire probe station, the device being tested is not shielded from the electromagnetic interference of probe station positioning motors and other sources of electrical noise on the station itself.
An alternative approach to controlledenvironment enclosures for probe stations is a compact, integrated enclosure as exemplified in an article by Yousuke Yamamoto, entitled "A Compact Self-Shielding Prober for Accurate Measurement of On-Wafer Electron Devices," appearing in IEEE Transactions on Instrumentation and Measurement, Volume 38, No. 6, Dec, 1989, pp. 1088-1093. This controlled-environment enclosure is very compact since it is part of the probe station structure and encloses only the wafer-supporting surface of the chuck and the probe tips. While the small, integral enclosure solves some of the aforementioned problems of the larger enclosures, it is incapable of maintaining any electromagnetic or hermetic seal during relative positioning movement between the chuck wafer-supporting surface and the probe tips along the axis of approach by which the probe tips and chuck approach or withdraw from each other. Such a drawback is particularly critical with respect to thermal testing requiring a dry purge gas, since each repositioning of the wafer and probe relative to each other opens the enclosure and therefore requires re-purging. Moreover no individual probe tip movement to accommodate different contact patterns is provided with such an enclosure, thus sacrificing flexibility of the probe station to test a wide variety of different devices.